Numerical control machines are designed to automatically perform milling, grinding and drilling operations. In some operations a numerical machine may drill or countersink. In others operations the drilling and countersinking of a hole may be in a single step. The inventive hydraulic stop may be used in a drilling operation, a countersinking operation or a combined drilling/countersinking operation. The inventive hydraulic stop is specifically designed to be used where the true location of a surface is unknown with respect to the program start point of a numerical control machine. If the true location of the work surface is not known, in some cases to 0.01 inch (0.0254 centemeter), then the depth of the hole or the depth of the countersink may not be within the tolerance required. Further, if the true location of the surface of the part is unknown, with respect to the program start point, the spindle of the numerical control machine may override beyond the expected stroke causing damage to the machine, part, or holding fixture.
The present invention is a self-contained automatic hydraulic stop which will act as a sensor and determine the true location of the surface of a work piece, permit accurate drilling or countersinking to a predetermined depth, provide protection for accidental spindle override to prevent damage to the tool, part, and holding fixture and reset itself without operator assistance for next operation.